The present invention relates to an injection unit for injection of a first fuel and a second fuel in a combustion space.
A way of reducing the discharge of emissions from combustion engines is to inject the fuel at a very high pressure. A so-called “common rail” system is widely used to effect injection at a high pressure in the combustion spaces of a diesel engine. A common rail system comprises a high-pressure pump which pumps fuel at a very high pressure to an accumulator tank (common rail). The pressure in the accumulator tank during operation may be of the order of 350-1600 bar. The fuel in the accumulator tank is intended to be distributed to all of the engine's cylinders. The fuel from the accumulator tank is injected into the combustion spaces of the respective cylinders via electronically controlled injection units. The injection units comprise valves which have to be able to open and close very quickly. The injection units are controlled by an electrical control unit which calculates substantially continuously the amount of fuel to be supplied to the respective cylinders on the basis of information about various parameters of the engine, e.g. load and speed.
There is increasing interest in using more than one fuel in combustion engines. It is for example of advantage to be able to begin a combustion process with an initial fuel which is readily ignitable and to end with a main fuel which is less readily ignitable, in which case the thermal energy arising from the ignition of the readily ignitable first fuel is used to ignite the less readily ignitable main fuel. This makes it unnecessary to use other types of additives to raise the ignitability of the less readily ignitable main fuel.
Injecting two fuels at high pressure in a combustion engine usually involves using two separate fuel supply systems, viz. a first fuel supply system with a first high-pressure pump which pumps the first fuel to a high pressure in a first accumulator tank (common rail), and a second fuel supply system with a second high-pressure pump which pumps the second fuel to a high pressure in a second accumulator tank (common rail). Thereafter the two fuels can be injected at high pressure from the respective accumulator tanks by means of suitable injection units. US 2002/0070295 refers an example of such an injection unit.